If the burning of fossil fuels is forcing the Earth to warm up, the rapid rise in sea levels that some expect from the thermal expansion of the oceans has yet to show itself clearly.

Ahead of this week's global warming conference in The Hague, Pacific nations were told about the results of a scientific reassessment of historical tide-gauge data in their region.

The study found that Pacific-wide sea levels had risen at an average rate of about 0.8 millimetres per year. The trend was measured using only those recording stations with hourly data stretching back more than 25 years.

Dr Wolfgang Scherer, director of the National Tidal Facility (NTF) of Flinders University, South Australia, which undertook the review, told BBC News Online that the much larger increases in global sea level predicted by some climate models were not apparent in their regional data.

"There is no acceleration in sea level rise - none that we can discern, at all," he said.

Slow response

The NTF study was presented to a recent forum of national leaders in the region, some of whom represent states that feel particularly vulnerable to climate change - notably, the low-lying atolls in the Pacific.

Dr Scherer said the NTF results fitted broadly with those produced by other studies around the world. And he said he was confident that the latest global climate assessment from the UN-sponsored Intergovernmental Panel on Climate Change (IPCC), due for release next year, would reflect these findings.

Dr Scherer said although there was mounting evidence that the oceans were getting warmer down to a considerable depth, it did not necessarily mean that any rise in sea levels that resulted from expanding waters had to accelerate. The rise could be just linear in nature.

"The ocean response time is clearly slow - perhaps of the order of a few hundred years," he added. "Even though the potential climatic effects of industrialisation might have been around for 150 years, let's say, in terms of ocean time that is relatively short.

"It is also true that if something does happen with the ocean, it will take a long time to turn it off, and that is why the precautionary principle absolutely has to apply."

Land movements

Although the NTF's work indicated at least short-term good news for low-lying countries, the Pacific Island Leaders Forum used its closing communiqué to reiterate concerns about the impact of climate change, and argued for early adoption of the Kyoto Protocol on greenhouse gas emissions.

But Dr Scherer said their worst fears might turn out to be exaggerated. Recognising that a number of climate models were predicting sea level rises of tens of centimetres by 2100, the scientist said some of the assumptions that underpinned the computer work and the global warming hypothesis in general would almost certainly need to be reviewed.

As with all climate studies, Dr Scherer said, uncertainty was the key problem. This could only be removed by a programme of on-going monitoring that used the latest and most sophisticated technology.

"For us, the major uncertainty is land movement. All the historical records of sea level measure only relative sea level. If you have a land mass that is rising, it will look like a lowering of sea level. Inversely, if the land is sinking, it looks like the sea is rising.

"And if we are making the linkage to climate, it is the absolute sea level that is important. So the next phase of the work we are doing will measure land movements."